1. Field of the Invention
The present invention relates to a plasma processing system that is able to measure a parameter for plasma control, a system and a method for measuring a parameter for plasma control, and a system for controlling a plasma processing system that is able to measure a parameter for plasma control.
2. Description of the Related Art
FIG. 15 shows a generally known plasma processing system 1000. The system 1000 includes a processing chamber U in which gases are ionized into a plasma. The plasma is used to apply a substrate G with a plasma process such as an etching or a sputtering. The plasma processing system 1000 includes a processing chamber 1005 in which the plasma process is performed. The chamber 1005 contains a susceptor 1010 on which the substrate G is mounted. The susceptor 1010 has an electrode 1015 embedded therein. The electrode 1015 connects to a high-frequency power supply 1020. The high-frequency power supply 1020 outputs high-frequency electric power, which applies a predetermined bias voltage in the processing chamber U. The bias voltage can increase the energy by which charged particles included in the plasma collide with the substrate G.
A matching box 1025 resides between the electrode 1015 and the high-frequency power supply 1020. The matching box 1025 includes a variable series capacitor C1 connected in series with an electrode 1015 via a power-supply line 1030a, a variable parallel capacitor C2 connected between a power-supply line 1030b and ground, and an inductor L. The matching box 1025 has a function of apparently matching the output impedance of the high-frequency power supply 1020 and load impedance that couples the load of the matching box 1025 and the internal load of the processing chamber 1005. The impedance matching can protect the high-frequency power supply 1020 and increase the use efficiency of the high-frequency electric power from the high-frequency power supply 1020.
The microwave plasma processing system 1000 has, however, capacitance Cs (parasitic capacitance) between the processing chamber 1005 and the susceptor 1010 or between the processing chamber 1005 and a power feeding rod 1010a supporting the susceptor 1010. At the high frequency, inductance L exists across which a significant voltage drop occurs in a power-supply line 1030a. The impedance thus generated downstream of the matching box 1025 (the high-frequency power supply 1020 is upstream of the box 1025) causes a significant portion of the high-frequency electric power from the high-frequency power supply 1020 to be consumed as the electric power is transmitted the power-supply line 1030a. Specifically, as the impedance downstream of the matching box 1025 increases, the high-frequency electric power available for the plasma control decreases.
Additionally, the conditions of the capacitive and inductive components generated downstream of the matching box 1025 depends on the dimension and material of the microwave plasma processing system 1000 or the like. The conditions also vary with the amount and type of the deposit formed on the wall surfaces of the processing chamber 1005 and the susceptor 1010 or the like. In this way, unpredictable change occurs in the impedance downstream of the matching box 1025. As the high-frequency signal is transmitted downstream of the matching box 1025, therefore, the high-frequency electric power experiences unpredictable loss.
To address the above issues, a feedback control system SS is proposed as follows (see, for example, JP 2005-116818). The system SS includes a measurement device 1035 and a control circuit 1040. The measurement device 1035 connects to the power-supply line 1030a between the matching box 1025 and the electrode 1015. The measurement device 1035 measures, for example, a voltage and power applied to the measurement position P. The control circuit 1040A compares the measured parameter and a desired target value. The comparison is used to feedback control the high-frequency power supply 1020.